Unable to Purchase Rank 4 of Mythic+ Essence from Thaumaturge Vashreen after Completing the "Keystone Master" Achievement
- I've completed a Mythic+ 15 and Thaumaturge Vashreen will still not sell me the essence.
- I have the Keystone Master achievement but the essence is still locked.
As the tooltip specifies, this Essence requires not just the general Keystone Master achievement for completing one +15 in time, but the Season 3 (or later) Feat of Strength for completing all +15 dungeons in time.
Battle for Azeroth Keystone Master: Season Three
Battle for Azeroth Keystone Master: Season Four
Please also ensure you reached rank 3 of this essence.